Heat transport in nano-environments adjacent to metal-liquid interfaces: Ultrafast photothermal study

Ultrafast photothermal/photoacoustic phenomena occurring at the interfaces of Ag nanoparticles in water and of Au electrodes in electrolyte solutions were investigated to understand heat transport in nano-environments. Ultraf ast lensing responses in a picosecond domain of the Ag nanoparticles showed bi-exponential decay with decay times dependent on surfactant concentratio n and pump wavelength as well. as sample temperature. Polarization independ ence confirmed with cartful intensity-normalization supported a thermal ori gin of the responses. An oscillation over 200 GHz was also observed and exp lained as an acoustic resonance. Transient reflectivity responses in a femt osecond domain of the Au electrodes showed electrochemical potential depend ence at the polarizable interfaces. Electrolytes in solution and interface modification by self-assembled monolayer were found to influence the depend ence. Interaction of non-thermalized electrons with interface molecules was suggested. Non-resonant coupling of electrons in metal with molecules in s olution could be considered as an ultrafast heat transport mechanism at the metal-solution interfaces.